Aquatic invasive species of greatest concern Some aquatic invasive species, such as the European green crab and zebra/quagga mussels, can have dramatic impacts on ecosystems, outdoor recreation, and the economy. European green crab Green crab pose a threat to Washington's native shellfish, which are important for recreational and commercial harvest as well as to the shellfish aquaculture industry, and native estuary ecosystems. Zebra & quagga mussels These species could cost taxpayers hundreds of millions of dollars a year and close down access to state waters for recreation and commercial opportunities. Northern pike Northern Pike are a highly invasive predator that is a serious threat to other fish species. Their voracious appetite for other fish and prolific spawning could cause great ecological and economic damage.